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(Circulation Research. 1996;78:238-243.)
© 1996 American Heart Association, Inc.

Articles

Distribution and Physiological Roles of ATP-Sensitive K⁺ Channels in the Vertebrobasilar System of the Rabbit

Tetsuhiko Nagao, Setsuro Ibayashi, Seizo Sadoshima, Koji Fujii, Kenichiro Fujii, Yusuke Ohya, Masatoshi Fujishima

From the Second Department of Internal Medicine, Faculty of Medicine, Kyushu University, Fukuoka, Japan.

Correspondence to Tetsuhiko Nagao, MD, PhD, Second Department of Internal Medicine, Faculty of Medicine, Kyushu University, Maidashi 3-1-1, Fukuoka 812, Japan.

Abstract The effect of an opener (levcromakalim) and a blocker (glibenclamide) of ATP-sensitive K⁺ (K_ATP) channels was investigated in the vertebrobasilar system of the rabbit. Arterial tension and membrane potential were measured by the isometric tension recording method and the microelectrode technique, respectively. Glibenclamide (10^-6 mol/L) depolarized the membrane and potentiated the contraction to histamine in vertebral arteries. The sensitivity to the relaxant effects of levcromakalim was in the following descending order: vertebral>proximal basilar>distal basilar>superior cerebellar arteries. Vertebral arteries were 50 times more sensitive to levcromakalim than were superior cerebellar arteries. The relaxation to levcromakalim was abolished by glibenclamide (10^-6 mol/L). Glibenclamide attenuated vasorelaxation to adenosine in proximal arteries (vertebral and proximal basilar) but not in superior cerebellar arteries. Levcromakalim (7x10^-8 mol/L) and adenosine (10^-5 mol/L) induced glibenclamide-sensitive membrane hyperpolarization in vertebral arteries but not in distal basilar arteries. These results suggest that K_ATP channels contribute to the determination of resting membrane potential and resting tone in vertebral arteries. Furthermore, there is a marked heterogeneity in the sensitivity to an opener of K_ATP channels, and the heterogeneity has a functional link to the mechanism underlying vasorelaxation to adenosine in the vertebrobasilar system of the rabbit.

Key Words: electrophysiology • regional difference • hyperpolarization • levcromakalim • glibenclamide

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